#include<bits/stdc++.h>
//if atcoder
//#pragma GCC optimize(3)
#define FastIO ios::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define int long long
#define I using
#define AK namespace
#define CSPS2025 std
I AK CSPS2025;
const int maxn=1e6+10,maxm=1e3+10,mod=998244353;
int n,m,x,y,u,v,w,res,ans,arr[maxn];
signed main()
{
    cin>>n>>m>>x>>y;
    u=(x+m-1)/m,v=(y+m-1)/m;
    if(u&1)
    {
        res=x%m;
        if(!res)
        {
            res=m;
        }
    }
    else
    {
        res=m-(x%m-1);
    }
    if(v&1)
    {
        ans=y%m;
        if(!ans)
        {
            ans=m;
        }
    }
    else
    {
        ans=m-(y%m-1);
    }
    if(res==ans)
    {
        cout<<"YES";
    }
    else
    {
        cout<<"NO";
    }
    return 0;
}